Using 12V stuff in my A5, need help!

Prokktor

Hi,

I happen to have tons of 12V PC Hardware lying around so I am exploring the possibility of using it in my A5:
(which only has a 300W noname power supply)

I do have 12V server power supplies so that part is covered.

Heat Bed: That should be no problem, it has a 12V connector and a standard 12/24V MosFet should do the trick.

Hotend: I have some 12V heating elements lying arround, I assume they are on/off only so the same procedure as with the hotbed should work.

Most Fans: Most of them can run all the time, so simply connect and forget.

Part cooling fan: I have extremely powerfull 40mm 12V Fans lying arround and like to use them, but here is the problem:

The A5 Fan only has + and - so I assume there is some kind of voltage regulator 0-24 on the mainboard. 
Even if I regulate it to 12V max via software, it still draws much more amps then the A5 Fan did and may overload the regulator...

What can I do to use the (supposed) 0-24V signal to control my high Amp 12V Fan? 
And are my other assumptions correct?

regards

Martin

Prokktor

News:
As far as I understand this Article about the MKS GEN L:
http://www.robotrebels.org/index.php?topic=769.0

The Mosfet for the controled fan is rated at 4.5A and actually identical to the extruder mosfet... so I can simply serialize 2 12V 1A fans and still be safe?

Samuel Pinches

Yes, except I don’t really recommend doing that... I would worry that if one fan stops spinning the power will be delivered to the stopped one, which could cause it to overheat and burn up.

Samuel Pinches

Better to fit a 24v to 12v step down voltage regulator ($3 on eBay) and then run both fans in parallel from there.

Prokktor

Ah interesting idea.

You are right, i'll bury the serialize idea in a deep hole^^

I ordered some PWM compatible MosFets yesterday so I can control the fan with 24V PWM signal, but it actually consumes power from my additional 12V power supply, that should also work and i dont have to check if the board holds up to the power demands of my fans. 

But ill buy some voltage regulators too :-)

EDIT:

Oh no that does maybe not work:
If I set my fan to 50% there will be a PWM signal with (average) 12 Volts wouldnt the step down regulator leave that at 12V instead of converting it to 6V like I need it?

Andre

The MosFETs for fans and heater on the controllers always are n-chanel. So they pulse the ground, not the Vcc.

If you use 12V for fans and hotend heater, connect the gnd(-) to the controllers. + from 12v PSU to + of fans (on the hotend heater it does not matter, wich wire you use for + and wich for -. gnd(-) of poth PSU have to be connected.

If only 12 or 5v Fan should be used, of course you can use a step-down-converter instead of second psu.

The heatbed I would not trust the boards MosFET. Use an external, as the current doubles If you half the voltage.

So you can use hybrid 24/12/5V systems easaly.

Prokktor

Ah thank you I already saw that on my mosfets input + and output + is actually the same, now I know why^^

Another crazy idea:
My new extruder Motor is designed for 12V, should it run to hot with 24V can I than connect 12V to my stepper driver instead of 24V? 

Samuel Pinches

@Andre  - thanks, I did not know that... thank you for sharing that!

Andre

@Prokktor: on an external MosFET input and output should be opto insulated, if you want different voltage.

Stepper motors are normaly not designed for a specific voltage but for a specific current.

The voltage given in the datasheet is simply the voltage that will result in the correct current by the resistance of the windings inside the motor (simplified). Thats important if you use a double-H-bridge to drive a stepper motor (for example this tiny geared stepper motors for Arduino, using 5V and a double-H-bridge).

If you use the common stepper drivers as they are on the controller board, there is a potentiometer. This gives a "reference voltage"

telling the driver which current to allow (alternativly in trinamics you can use spi to adjust the driver).

Of course the torque (and the heat a stepper motor products) depends of both voltage and current. So if the motor is too hot, you simply reduce current. A normal Nema 17 is allowed to temperatures around 100°C. So "too hot" is rearly reached. But its allways good to use only as much force as realy is needed, so reduce current.

In principle you can modify a stepper driver for a different voltage. But there is barly a need to do so ( I only had to do so once for a plotter from Fischertechnik. It was double-H-bridge controlled and used 6.8V in 1985. Modern Fischertechnik uses 9V, so the motors got hot. So I added an external double-H-bridge on 6.8V to the new fischertechnik controller to use it with the old Plotter. Very special scenario).